You’ll need at least three players and a deck of playing cards. You won’t need all the cards, but you will need to set aside the following:
JOKER: There is one Joker. If you draw the Joker, you are the Robber. Your objective is that the Guard will not shoot you, but will shoot a Customer instead. No one knows you are a Robber. Everyone assumes you are a Customer until you tip your hand.
JACK: There is one Jack. If you draw the Jack, you are the security Guard. Your objective is to shoot the Robber and only the Robber. If you shoot the Robber, you win. If you shoot anyone else, you lose. Everyone knows that you are the Guard; you wear a security uniform.
2-10: There are enough numbered cards for the remaining players to receive one. If you draw a numbered card, you are a Customer. Your objective is to not be shot. Therefore, if you can help the Guard identify the Robber, so much the better.